Only the Shadow Knows

Pulled the trigger and got the Q5 TDI Premium Plus for the lovely wife.
Just 140 miles old. One word: Amazing.

But one function has me stomped: The stop-start system stops working after a warm re-start (like when parking briefly at Starbucks), and refuses to switch off upon a full stop, even when the brake pedal is fully depressed.

Just a random guess: I think I may have a defective temperature sensor, because of items 2 and/or 3 on the list below:

Engine does not switch off

Before each stop phase, the system checks that certain conditions have been met. The engine will not switch off in the following situations, for example:

1. The engine has not yet reached the minimum temperature required for start/stop mode.
2. The interior temperature selected on the air conditioner has not yet been reached.
3. The exterior temperature is very high/low.
4. The windscreen is being defrosted.
5. The parking aid is switched on.
6. The battery charge is too low.
7. The steering wheel is close to full lock or the vehicle is being steered.
8. Reverse gear has just been selected.
9. The vehicle is on a steep gradient.

The question is: Has anyone on the forum experienced a recalcitrant start-stop function after a warm re-start, esp. when the AC is on? (The Q5 TDI seems to work well upon a cold-start after reaching normal temperature.)

Just curious. I have scheduled this girl to visit my Audi dealer next week for a diagnostic check. But knowing before-hand your experiences will be appreciated. Thanks!

Mrclopec

The start/stop system is awesome but from our experience can be very finicky when it comes to wether it wants to do it or not. There are so many different conditions that need to be met or it won't turn off. We found that if you have the A/C system on "Auto" and the temp turned all of the way to "LO" the car won't turn off. We've also found it will do it if we pull up to a light and have the steering wheel turned at a hard angle. I wouldn't worry too much about it.

Only the Shadow Knows

I live in Washington, DC. And it is a swamp. But what is surprising is that stop-start works properly when started from cold, but then refuses to engage after a warm re-start.

I can understand when the cabin temperature is set to an unbounded "LO", like you describe. See item (2).

In my case the AC was set with the temperature at 66 degrees and with recirculation on. The driver seat's heater typically on at "2". The outside temperate was 75 degrees which is unusually mild for Washington, DC.

I am not worried. I would be if the opposite would be true: if the stop-start system would force the engine off and hesitate when starting from rest on the middle of an intersection.

Like you said it is an awesome feature.

I will try to find out from the dealer if any codes are thrown by the engine management system pointing to the stop-start system being cancelled. (The dashboard does show the cancelled stop-start icon every time on a full stop, so the system recognizes the condition.) If there are no codes, and no TSB, then the dealer will be clueless.

And life goes on. Thanks!

lja36

one big determinant is the temperature of the various emission control catalysts... for the system to be emissions compliant, the catalysts need to be at a certain temperature. an idling diesel may blow cold (in relative terms) exhaust gases rendering it less efficient or the other way around... there are a gazillion sensors watching all this stuff... if there is a fault you will certainly be told... i plugged in a VAG-COM and I can see them monitoring over 500 parameters.

melland

Another factor is how long you were driving before you stopped at Starbucks. If you started the Q, drove only a couple miles, got coffee, and hopped back in to drive away - the engine may have been warm but not fully warmed up to hold the temp needed to immediately engage start-stop again.

I've noticed the weather's really affected mine lately due to having the air conditioner pumping so hard. Engine will shut down at a traffic light in 90+ degree heat but it will start back up before I let my foot off the brake in order to keep the car cool.

idale

I expect your system's working fine, as the car will start cooling off when it's no longer running (and the inside temperature drifting, etc.). If you stop really quickly then start-stop may be able to still satisfy all the multitude of requirements right away, but more than a minute or two and it's likely it'll take a few minutes to get everything ready to go again.

I can vouch for the system being potentially ready to go right away after a warm start since every once in a while when dropping off the kids at daycare or picking them up, my engine will stop when stopping to turn out onto the street. It's uncommon but does happen. Most of the time, though, it doesn't do that and isn't ready to shut off again for several minutes.

With the number of criteria that have to be met, it's a bit of a mystery at any given moment what all is preventing start-stop from activating. Obviously if the climate control is still trying to achieve temperature, or the car's running an active regen cycle, or if everything's not yet warmed up, then it won't activate, but there's times that I would expect all the criteria would likely be met, yet the engine's still running. It's just a matter of the criteria actually haven't been met as I can't see all the internal system temperatures and timers and everything else it's checking.

Only the Shadow Knows

Thank for all the replies. Much appreciated.

But it is actually not working properly. i understand the prerequisites fully, as I listed only some of them on my original post.

I have made an appointment with my Audi dealer on Monday 22 June, and expect a full diagnostic of the stop-start system by zooming-in on the codes thrown by he Q5's central management system. That should be the "tale of the tape".

Here i what I have written a instructions to my advisor, so it is crystal-clear, when I drop the lovely:
I will report back on the findings to anyone who is interested. At least from the replies, the stop-start being "twitchy", I see that i may be a one-off, and it is not a generic Q5 TDI problem across the board.

Thanks to all. Will come back later next week.

NorthValley

So you have outside temps of between 75 and 90 with the aircon set to a cool 68 on a fairly high fan speed and yet you have the heated seats on? Likely the system is confused! ;-)

Only the Shadow Knows

LOL! on your comment.

This is normal.

Cool the cabin, warm the seat, mildly. Helps with back aches on long drives. And increases cabin comfort.

I see no confusion on my part; but if there is one on the programming of the start-stop system, the Audi Tech will be able to tell.

i expect then proof that by turning the seat heat the system operates as programmed.

Lets wait and see.

BlackSVT

My experience after ~40k miles w/the 3.0T is that heavy A/C demand (which your settings are...) will always prohibit Stop-Start. I almost wonder if your A/C is working properly because if I set mine to 68 Auto and recirculate, I'll be frozen out in no time, and I like it cool.

Try setting A/C to something less demanding (just as a test), say 73, turn the Recirc off, and put the fan on 3 or 4, then see what happens w/Stop-Start. I find that if Auto is forcing a fan speed higher than 4 to heat/cool, then Stop-Start will almost never activate.